1. Field of the Invention
The present invention relates to a sub-frame structure of a motor vehicle, and in particular to a sub-frame structure of a motor vehicle for use in connecting parts to a vehicle body.
2. Background Art
Side frames and other motor vehicle sub-frame structures for connecting parts, such as a suspension system, engine or the like, to the vehicle body are known.
A sub-frame structure using upper and lower members joined together to form a closed section has been proposed. However, it is difficult for this type of sub-frame structure to establish great strength with a small cross sectional area. In addition, since flange portions necessary for joining the upper and lower members extend outward from the sub-frame, it is difficult to efficiently utilize the space around the sub-frame.
Japanese Patent Unexamined Publication No. 9-86435 discloses a sub-frame structure made of tube members as a whole. Although this sub-frame does not encounter the above problem, the tube members are difficult to deform, especially into a complex configuration including consecutive small bends or curves with small radii of curvature and small corners. This is a serious problem for a sub-frame whose structure should be adjustable over a wide range depending on the positional relationship with the parts around it.
More specifically, in the case of a front sub-frame for a front engine front wheel drive (FF) type motor vehicle for example, a pair of longitudinally extending frame members are required to be widely spaced apart on the front side so as to provide a space for an engine and a transmission therebetween, and to be closely spaced on the rear side so as to improve the characteristics of a suspension system to be mounted on the rear side. Making this type of sub-frame structure entirely of tube members is difficult because it is hard to deform the tube blanks so as to have bends for making the transition from the widely spaced portion to the closely spaced portion.
Further it is difficult to directly mount parts on a sub-frame structure made of tube members. Therefore, the parts must be mounted by the brackets and this increases the number of parts required.
It is therefore an object of the present invention to provide a sub-frame structure of a motor vehicle that is easily adjustable into a desired configuration and that facilitates the mounting of parts.
The present invention achieves this object by providing a sub-frame structure of a motor vehicle comprising: a pair of side frame sections extending in a longitudinal direction of the vehicle at predetermined lateral spacing and each side frame section including a laterally inward bend; and a cross member section connecting front ends of the side frame sections; wherein the cross member section and end portions of the side frame sections including the front ends of the side frame sections connected to the cross member section are integrally formed of a deformed tube member and remaining portions of the side frame sections including the bends are formed of a closed section member fabricated by joining a plurality of members at flanges.
In a preferred embodiment of the present invention, the sub-frame structure further includes mounts for suspension arms provided in the closed section member.
In another preferred embodiment of the present invention, the mounts are provided in the bends.
In another preferred embodiment of the present invention, each mount comprises a mounting member having an inverted U-shaped member oriented to open laterally.
In another preferred embodiment of the present invention, the sub-frame structure comprises reinforcing members provided forwardly of the mounting members.
In another preferred embodiment of the present invention, the sub-frame structure comprises reinforcing members extending from the mounting members into the side frame sections.
In another preferred embodiment of the present invention, the reinforcing members are positioned at upper regions of the side frame sections.
In another preferred embodiment of the present invention, the sub-frame is a front sub-frame installed on a front side of the vehicle, an engine and a transmission being placed between a part of the side frame sections made of the deformed tube member.
In another preferred embodiment of the present invention, the sub-frame is a front sub-frame installed on a front side of the vehicle, an engine and a transmission being placed side-by-side between a part of the side frame sections made of the deformed tube member.
In another preferred embodiment of the present invention, the sub-frame structure comprises reinforcing brackets that join the end portions of the side frame sections to end portions of the cross member section.
In another preferred embodiment of the present invention, the sub-frame structure further comprises a pair of connecting brackets for connecting ends of the side frame sections to a dash lower panel and a side sill of the vehicle body provided at ends of the side frame sections.
The above and other objects and features of the present invention will be apparent from the following description of preferred embodiments of made with reference to the accompanying drawings.